In a voice collection method, disclosed in Patent Document 1, an output from each of two microphones is divided into a plurality of frequency domains. The difference in parameter values of sound signals, arriving at the microphones, and which are variable by reason of microphone positions, is detected. Based on this difference in detection, frequency components of the respective sound signals are selected for sound source separation. The sound of interest is distinguished from the sound not of interest based on the difference in their frequency characteristics. The sound not of interest is suppressed in the frequency domain. The output frequency components of the respective sound signals are synthesized into sound source signals.
In a noise removal method, disclosed in Patent Document 2, an input time domain signal is separated into a plurality of subcomponents by a signal separation unit. The noise contained in the subcomponents, resulting from the signal separation, is estimated by a noise estimation unit, using the subcomponents. A noise removal unit removes the so estimated noise from the subcomponents.
Patent Document 1:
    JP Patent Kokai Publication No. JP2000-081900APatent Document 2:    JP Patent Kokai Publication No. JP2005-308771A